Currently, multi-user (MU) transmission has become a hotspot in development of a wireless local area network, for example, an MU multiple-input multiple-output (MU-MIMO) system and an orthogonal frequency division multiple access (OFDMA) system. Because of introduction of an MU transmission manner, to ensure that effective communication is performed between an access point and multiple stations using a specified resource block, overheads for indicating a resource to each station by the access point sharply increase.
For example, as shown in FIG. 1, an access point indicates resources to users/user groups in a station one by one in order to indicate information about a resource block that is used when the station sends a Media Access Control (MAC) frame to the access point or receives a MAC frame sent by the access point. A resource indicator for a single user (SU) may include a partial association identifier (PAID) that is used to identify a station, a downlink/uplink type that is used to indicate whether a resource block belongs to a downlink frame or an uplink frame, a modulation and coding scheme (MCS) that is used to indicate a modulation and coding scheme, a number of space-time streams (NSTS) that is used to indicate a quantity of space-time streams that are used, low-density parity-check code (LDPC) that is used to indicate whether an LDPC coding manner is used, a space time block code (STBC) that is used to indicate whether STBC is used, and the like. Similarly, for a resource indicator for an MU group, a PAID may be a group ID (GID) that is used to indicate an identifier of the user group.
The access point needs to use 60 bits to indicate a resource to a SU, and needs to use 84 bits to indicate a resource to a user group. However, a size of a response frame such as a block acknowledgement (BA) frame or an acknowledge (ACK) frame is only from 10 to 30 bytes (where 1 byte=8 bits). It may be learned that, in comparison with an actual size of the response frame, overheads are extremely large when the access point indicates a resource to such a response frame. Therefore, in other approaches, resource utilization is not high when an access point indicates a resource to a station.